'Waterproof' is one of those words! My newest all-singing all-dancing battery-heated winter gloves are, they say, so's my preferred winter over-everything-jacket, designed for offshore fishermen (height of sartorial elegance, that). They're good, but they aren't 100% after say 6 hours of a pissy wet day on unfaired bikes.
So with mags . . . A standard K2F should be 'shower-proof' using the clothing analogy, and can be made more so with the use of sheathes over the HT pick-ups (and advance/retard cable entry if fitted), with silicon goo thrown in. Goo on the HT pick-up gaskets too. But there are ventilation holes in the mag body underneath, and the contact breaker end will be more or less shower- or water-proof depending on what end cover you have.
A Comp model shouldn't have the ventilation holes underneath, has screw-on pick-ups and cb cover with a breather extension to which a pipe can be attached to take the exit point up and away. It is a better starting point than the standard version because screw-on is always going to be better than clip-on, but crossing rivers in spate would probably still be risky!
Haven't seen the Wader label applied to a K2 mag, I think it's pretty well an NC1 single cylinder tag, but may be wrong.